I think he did it and is cunning enough to twist the facts to look like a "false confession" in order to be acquited, get back to the US and seek his next victim.
1. It was an accident.
2. It's only 2nd degree murder BECAUSE IT WAS AN ACCIDENT.
THAT'S why he left a ransom note....A ransom note for a DEAD GIRL? It was "Hard Evidence" that it was an accident in case he got caught and he jumped at the chance to say it was an accident but said "no comment" to many other questions.
But the note doesn't make any sense. It was too long and it was non-sexual and violently directed at the parents....at money and power. It shows "absolutely no love" for the girl. She's just the tool to destroy the Ramseys.
Have little doubt that there will be more cases being dusted off......going waaaaaaay back to his youth.
That has happened before - a "false" confession that gets thrown out. He could well have read about them.